This invention relates to a plastic card having metallic luster.
Presently, an extremely great number of plastic cards such as identification cards, bank cards, membership cards, credit cards, etc. are being utilized. These cards are used as they are, or function as magnetic cards of which various kinds of information are recorded by magnetic recording methods.
In recent years, several cards of beautiful exterior appearance having metallic luster have been proposed. A card of this type of the prior art has a structure in which a printed layer with metallic luster is formed by printing a plastic sheet, with printing ink having a metallic luster pigment dispersed therein by off-set printing or screen printing techniques, and having a transparent plastic sheet laminated on the printed layer. Another example of such a card has a structure in which a metallic luster powder layer is formed by adhesion of metallic powders with an adhesive onto a plastic sheet, and a transparent sheet is laminated on the powdery layer.
However, it is difficult to obtain sufficient metallic luster because of technological difficulty in providing a thick metal luster printed layer or metal luster powder layer. Another difficulty is that a transparent plastic sheet can be readily peeled off due to insufficient bonding between the transparent plastic sheet and the metal luster printed layer or the metal luster powder layer.
To overcome these aforementioned difficulties, an alternative structure in which a metal luster plastic sheet is prepared by dispersing a metal luster pigment into a transparent plastic by Kneading, and subsequently laminating a transparent plastic sheet onto the metal luster plastic sheet has also been proposed. However, problems still exist due to the greater particle size of metal luster pigments, as compared with the common coloration pigments, and also to very poor dispersibility of the aforementioned pigments in plastics.
More specifically, when the pigment concentration is increased to improve the metal luster, the dispersibility of the pigment decreases, whereby irregularities are liable to occur in the metal luster color formation, and the problem of the pigment adhering to a rolling roll during the preparation of the sheet causes inconvenience in production procedures. Further, the physical properties such as tensile strength and impact resistance of the sheet are lowered. Therefore, a good plastic card has not yet been produced.
Also, because of the aforementioned difficulty of obtaining a card with a high pigment concentration, the resultant card may sometimes be semi-transparent when made to the conventional thickness ranging between 0.7 and 0.8 mm. Hence, when using such a card in, for example, various card treatment devices, optical detection of the card position may not be possible because of the excessively high light transmittance of the card.